The present invention relates to a special optoelectronic light branching element or diplexer for a multiplexdemultiplex modes which unit is required in some modern broad band communication systems, particularly in great numbers. The invention is directed to a specific light branching unit which has a first light connection that is bidirectionally operated and second and third light connections which are each unidirectionally operated, the unit is composed of a solid block of glass having a straight groove along the surface in which a glass fiber which has three glass fiber regions is embedded as a light waveguide, a first light connection is optically coupled to the first glass fiber region and a third light connection is connected to the third fiber region. At the second fiber region, which extends between the first and third regions, the embedded glass fiber is separated by a partially transmitting mirror which extends in a plane obliquely relative to the glass fiber axis and the block and forms a second light connection at which a perpendicular to the plane of the mirror forms an acute angle of incidence with the axis of the neighboring glass fiber coming from the first connection. A light sensitive location of a light receiving semiconductor unit is secured on the block in the second glass fiber region close to the second light connection without the insertion of any additional glass fibers extending from a gap to the light sensitive location. The mirror is a light waveguide filter such as a vapor deposit layer which preferably reflects light of a first light wavelength to a receiving portion or location of the light receiving semiconductor unit while allowing light of a second light wave length to pass therethrough so that light can move between the first and third light connections.
A light diplexer unit, or branching unit, which has a light reflecting surface for a particular light wavelength is disclosed in U.S. Pat. No. 4,439,005, which claims priority from German Patent Application No. 28 40 602. This unit comprises a circular segment in cross-section and has a long tubular metal sleeve as a capsule. In addition to an electrical light receiving semiconductor element or member, two purely optical connections are also applied to the three light connections so that the light reception semiconductor member is attached in the wall of the capsule. According to this disclosure, the mirror is at an angle of 45.degree., or half of a right angle, relative to the axis of the fibers.
A few critical investigations of such a light diplexer have shown that at least for many applications they should be decidably improved in at least two regards. The first of these is the manufacturing of the block as well as the capsule, and above all, the mounting of this block precisely in its rated position in a capsule as well as the fixing of the light reception semiconductor element proximate to the mirror on the block should be considerably simplified. The second improvement is that the disturbances, particularly echoes, of the electrical signals obtained at the light reception semiconductor element which strongly occur in a very unpleasant way with high modulation frequencies of the light formed by the fiber should be eliminated in an optimum, elegant and simple manner.
Together, these two disadvantages are the important prerequisites in order to be able to employ large item numbers of the light diplexer in, for example, an opto-electronic ISDN broad band switching system as an interface between a bi-directionally light-conducting exterior glass fiber connected to a first light connection on the one hand and the electronics on the other hand.
An extremely great number of light diplexer units which are similar in some respects are known. Examples of these are disclosed in U.S. Pat. No. 4,564,260, which claims priority from German Patent Application No. 29 21 035, particularly FIG. 2 of this patent; in article by Miyauchi et al, Opt. Lett., Vol. 5, No. 7, July 1980, pages 321-322; and articles in NtzArchiv, Vol. 5, 1983, pages 97-99, particularly FIGS. 1 and 2, J. of Lightwave Techn., Vol. LT-2, No. 4, August 1984, pages 369-378, particularly FIGS. 1(a) and 6, and J. of Lightwave Techn., Vol. LT-2, No. 5, October 1984, pages 675-681.
All of these known light branching or diplexing units respectively comprise a capsule having pure optical elements at the light connections. In these known light diplexer units, namely the three external connections at the capsule are respectively only external glass fiber connections in that light is used therein as information carrier in a connecting path of the communication system up to the peripheral subscriber station. Such an operation of a connecting path, however, is frequently not favorable. Often, it requires too high a finemechanical and optical precise outlay, particularly in view of the many external glass fiber connections, namely not only at the information connection of the many light diplexer units, but also especially in the line sections, which are usually extremely numerous in such a communication system, particularly in a public switching system, between the light diplexer units and often several thousand subscriber stations. The invention should allow this outlay to be avoided.
It is known from various publications to make the mirror in the glass fiber or, respectively, in the block steeper than 45.degree.. For example, an angle of incidence smaller than 45.degree. in order to obtain an especially good optical coupling to an additional glass fiber whose axis describes an angle smaller than 90.degree. with the axis of the embedded glass fiber. Examples of these are from European Application No. A 37 057, as well as U.S. Pat. No. 4,541,159, which claims priority from German Application No. 32 36 149.
A measuring instrument comprising light diplexer units for error location in long glass fibers is known from an article from ntz, Vol. 31, No. 2, February 1978, pages 144-146 which discloses a capsule-free light diplexer unit comprising one purely optical, one glass fiber connection and two electrical connections formed by a light transmission and a light reception semiconductor component at the second and third light connections. However, the light diplexer unit disclosed therein is too unwieldy for employment in large communication systems, especially when the numerous light diplexer units are to be accommodated in the tightest space in a common cabinet.
There is an extremely high number of additional references with respect to the technological background for light diplexer or branching units and opto-electronic communication systems. Examples of these are: U.S. Pat. No. 4,317,699, which is based on German Application No. P 28 51 679; German OS 28 51 696; German OS 29 03 288; German OS 29 18 403; U.S. Patent Application Ser. No. 246,100, which issued on Jan. 20, 1987 as U.S. Pat. No. 4,637,682 claims priority from German Patent Application No. 30 12 184; the above mentioned U.S. Pat. No. 4,541,159; British Patent No. 2,020,447; U.S. Pat. Nos. 3,953,727; and 4,165,496; an article from Appl Opt., Vol. 20, No. 18, 15 September, 1981, pages 3128-3135, particularly FIGS. 1, 5 and 9; an article from Siemens Forsch. u. Entw.-Ber., Vol. 12, No. 5, 1983, pages 332-339, particularly FIG. 2; an article from Fiber and Integr Opt., Vol. 4, No. 4, 1983, pages 339-372, particularly FIGS. 2, 18, 9 and 17; a paper from 10th European Conference on Opt. Commun. (ECOC), Stuttgart, 3-6 September, 1984/Conference Proceeding, pages 262-263, particularly FIG. 2; an article from SPIE 468 Fiber Optics '84 (SIRA), 1984, pages 68-73, particularly FIGS. 4 and 8; a paper from European Conference of Opt. Commun. (ECOC), Cannes, 21-24 September 1983/Conference Proceedings, pages 305-314, particularly FIGS. 4 and 7; a paper from Journees d' Electronique, Lausanne, 1982/Conference Proceedings, pages 89-111, particularly FIGS. 1(c), 12, 14(a,b,c) and 19; a paper from 6th European Conference on Circ. Theories and Design, Stuttgart, 6-8 September 1983/Conference Proceedings, pages 315-317, particularly FIGS. 6 and 7; and a paper from U.R.S.I., Kleinheubacher Tagung, 3-7 October 1983/Kleinheubacher Berichte, No. 27, pages 13-29, particularly FIGS. 1 and 5(b).
Detailed teachings regarding the manufacture of light diplexer or branching units, particularly with regard to the blocks and mirrors, are contained in several of the above-mentioned publications.
Moreover, light receiver semiconductor members, for example photodiodes, and light transmitting semiconductor members, for example, IRED diodes, are extremely well known to a person skilled in the art. Many references also disclose that the ends of glass fiber light lines might frequently be directed with extreme precision to the optically active location of such a semiconductor element with a long-term stability, frequently even with extremely high tolerances of plus or minus a few .mu.m, sometimes of even plus or minus 0.1 .mu.m, in order to achieve good optical coupling therewith. An example is from the European Application No. A 137 485.